Linear pipe recovery/lay tensioners and methods of using same

ABSTRACT

Linear pipe recovery/lay tensioners can include one or more pivot assemblies for rotatably moving an upper track away from a lower track to facilitate placement of a pipe segment between the two tracks. In addition, or alternatively, the tensioners can include one or more hydraulic cylinders that provide flexible suspension to the upper and lower tracks so the tracks can move and rotate as necessary due to differing pipe segment shapes. In addition, or alternatively, the upper and lower tracks include one or more gripping pads having one or more gripping members that can be sheathed by a compliant member until such time as the pipe segment compresses the compliant member causing the gripping member(s) to protrude from the compliant member and engage the pipe segment. Rotation of the tracks is controlled by a hydraulic pump capable of rotating the tracks at the same rate or at different rates.

RELATED APPLICATION

The present application is a continuation-in-part of, and claimspriority to, U.S. Non-Provisional patent application Ser. No.13/357,007, filed Jan. 24, 2012.

BACKGROUND

The invention is directed to roller assemblies for linearly transportingone or more pipe segments, or joints, such as pipelines, and inparticular, to linear pipe recovery/lay tensioners for pulling a portionof pipeline from the ocean to be recovered on an offshore lay-barge andfor laying pipeline from an offshore lay-barge and onto the ocean floor.

Linear pipe tensioners are generally known in the art. These devices aregenerally installed on a ship or lay barge to facilitate laying orretrieving pipe, such as pipelines and other pipe segments. Linear pipetensioners are designed to maintain a constant tension on the pipe whilethe pipes are being lowered into, or retrieved from, the sea duringoffshore pipe laying operations.

Broadly, linear pipe tensioners consist of an upper and a lower track,each supported in a frame assembly. Pneumatically actuated squeeze bagswithin the track loops apply squeeze forces on the tracks holding thepipe. The tracks are driven by hydraulic motors through cage-mountedgear reducers. The upper track can be adjustable vertically for handlingof various sizes of pipe. An electronics package comprising a controlconsole and PLC operates the electronic components necessary for systemoperation. Pressure to track drive motors is controlled to maintain pipetension within selected limits.

Two or more linear pipe tensioners can be arranged in series to providethe desired or necessary tension in the pipeline for laying orretrieving the pipeline.

In operation, generally, when an operator sets a tension value andstarts the linear pipe tensioner, stepper motors mounted on thehydraulic pumps are rotated under command from the electronic controlsystem, Greater rotation increases the volume of hydraulic fluid fromthe pumps to the motors. The motors then increase the amount of tensionagainst the pipe.

Load cells, mounted between the linear pipe tensioners and theirbedplates, transmit a signal proportional to the amount of tensionagainst the pipe to the electronic control system. When the signal fromthe load cells balances the signal from the tension, a preset circuitthe stepper motors stop rotating and hold their positions. This keepsthe hydraulic pumps on a stroke which produces sufficient pressure tohold the desired tension. Small movements of the lay-barge do notproduce any significant change in the tension. Movements beyond apre-set dead-band will produce changes in tension transmitted back tothe control system. The tension command will become unbalanced and thecontrol system will drive the pumps producing pressure to the hydraulicmotors to bring the tension back into line.

SUMMARY OF INVENTION

The linear pipe tensioners disclosed herein facilitate one or both ofrecovery of pipe segments from their locations of installation, andinstallation of the pipe segments in their locations of installation. Incertain embodiments, the linear pipe tensioner comprise upper and lowerframes, the upper frame having an upper track assembly and the lowerframe having a lower track assembly. The upper and lower frames arepivotally connected to each other to facilitate movement of the upperframe and, thus, the upper track, between a closed position and aplurality of opened positions. Movement of the upper frame facilitatesplacement of a pipe segment between the upper and lower tracks.

In other certain embodiments of the linear pipe tensioners, the upperand lower frames are not required to be pivotally connected, althoughthe upper and lower frames can be pivotally connected. In theseembodiments, one or both of the upper or lower tracks are operativelyassociated with one or more cylinders that permit vertical and/orrotational movement of one or both of upper and lower tracks.

In still other embodiments of the linear pipe tensioners, the upper andlower frames are not required to be pivotally connected and the one ormore cylinders are not required to be present, although one or more ofthese features can be included. In these embodiments, one or moregripping pads is operatively associated with either the upper or lowertracks. One or more of these gripping pads comprise a compliant memberhaving a slot and a gripping member disposed within the first slot suchthat compression of the compliant member causes at least a portion ofthe gripping member to be exposed from the slot. In so doing, thegripping member engages a pipe segment to facilitate linear movement ofthe pipe segment through the linear pipe tensioners. In anotherembodiment, these gripping pads comprise a compliant member having aplurality of slots with a plurality of gripping members disposed withinthe slots, where the plurality of gripping members may have a variety ofshape, material, or layout characteristics designed to facilitategripping the pipe.

In additional embodiments, which may or may not include one or more ofthe features discussed above, two drive assemblies move the trackswhich, in turn, linearly move a pipe segment through the linear pipetensioners. The two drive assemblies are operatively associated with ahydraulic motor or pump and a valve. The valve facilitates placing thedrive assemblies in either series or parallel such that the two driveassemblies can rotate at substantially the same rate or at differentrates. In these embodiments, the structural components identified abovein this Summary can also be part of the linear pipe tensioners, althoughthey are not required.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description of various embodiments usable within thescope of the present disclosure, presented below, reference is made tothe accompanying drawings, in which:

FIG. 1 is a side view of one specific embodiment of a linear pipetensioner disclosed herein.

FIG. 2A is a front view of the linear pipe tensioner shown in FIG. 1

FIG. 2B is a front view of the linear pipe tensioner shown in FIG. 2Ashowing the top track pivoted to an open position for receiving asegment of pipe.

FIG. 3 is a partial cross-sectional side view of a roller assembly ofthe linear pipe tensioner shown in FIG. 1.

FIG. 4 is a perspective view of the roller assembly of FIG. 3.

FIG. 5 is a perspective view of a gripping pad of the linear pipetensioner shown in FIG. 1.

FIG. 6 is a longitudinal side view of the gripping pad of FIG. 5.

FIG. 7 is a lateral side view of the gripping pad of FIG. 5.

FIG. 8A is a perspective view of the gripping member plate of thegripping pad of FIG. 5.

FIG. 8B is a top view of the gripping member plate of FIG. 8A.

FIG. 8C is a partial cross-sectional view of the gripping member plateof FIG. 8A taken along line 10-10 shown in FIG. 8B.

FIG. 9A-9C is a perspective, top, and partial cross-sectional view of analternative embodiment of a gripping member plate used in FIG. 5.

FIG. 10A-10C is a perspective, top, and partial cross-sectional view ofanother alternative embodiment of a gripping member plate used in FIG.5.

FIG. 11 is a schematic of one specific drive motor flow control systemfor actuating the drive assemblies of the various linear pipe tensionersdisclosed herein.

FIG. 12 is a schematic of another specific drive motor flow controlsystem for actuating the drive assemblies of the various linear pipetensioners disclosed herein.

While the invention will be described in connection with the preferredembodiments, it will be understood that it is not intended to limit theinvention to that embodiment. On the contrary, it is intended to coverall alternatives, modifications, and equivalents, as may be includedwithin the spirit and scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring now to FIGS. 1-10, in one specific embodiment linear pipetensioner 10 includes frame 12. In this particular embodiment, frame 12comprises upper frame member 13 and lower frame member 14 rotatablyconnected to each other by pivot assembly 15. As shown in FIGS. 1, 2A,and 2B, pivot assembly 15 comprises two hinge members comprising pins 16inserted through brackets 17, and cylinder 18. Pivot assembly 15 permitsthe movement of upper track assembly 20 along the trajectory of thearrow shown in FIG. 2B to facilitate insertion of a pipe segment (notshown) within space 30 between upper track assembly 20 and lower trackassembly 40.

Although frame 12 is shown as having upper and lower frame members 13,14 pivotally connected by pivot assembly 15, it is to be understood thatframe 12 is not required to have these components. To the contrary,frame 12 may be a structure that is not capable of being opened tofacilitate insertion of a pipe segment.

Upper track assembly 20 is operatively associated with upper framemember 13 by front axle 21 and back axle 22 which are rotatable by driveassembly 23 being operatively associated with upper track 24. As shownin the embodiment of FIGS. 1-10, drive assembly 23 is directly connectedto front axle 21. Upper track 24 is disposed on a plurality ofsuspension assemblies 60, front axle 21, and back axle 22. Discussed ingreater detail below, track includes a plurality of gripping pads 75 forengaging a pipe segment to facilitate pulling the pipe segment throughlinear pipe tensioner 10 in a linear direction.

Lower track assembly 40 is operatively associated with lower framemember 14 by front axle 41 and back axle 42 which are rotatable by driveassembly 43 being operatively associated with lower track 44. As shownin the embodiment of FIGS. 1-10, drive assembly 43 is directly connectedto front axle 41. Lower track 44 is disposed on a plurality ofsuspension assemblies 60, front axle 41, and back axle 42 and includes aplurality of gripping pads 75.

Broadly, in operation of linear pipe tensioner 10, a segment of pipe(not shown) is disposed within area 30, such as by pulling the pipesegment linearly through area 30 or by pivoting upper track assembly 20to the opened position shown in FIG. 2B, disposing the pipe segmentwithin area 30, and then closing upper track assembly 20. As a result,gripping pads 75 engage the pipe segment above and below the pipesegment. Drive assemblies 23, 43 are activated causing tracks 24, 44 andmove around front and back axles, 21, 41, 22, 42. In so doing, the pipesegment is pulled linearly through area 30 causing the pipe segment tobe removed from its installed position to its recovered position. Asmentioned above, the installed position can be on the ocean floor orwithin an earthen formation and the recovered position can be on alay-barge or other ocean-going vessel or on a terrestrial location suchas a truck or on the ground of a worksite. Drive assemblies 23, 43 mayutilize variable frequency AC or DC electric drive motors, or hydraulicdrive motors, depending on available power sources or needs.

In one particular embodiment, drive assembly 23 and drive assembly 43are operatively associated with a hydraulic drive motor flow controlsystem. The drive motor flow control system permits synchronization ofrotation of front axles 21, 41. The simultaneous action of driveassemblies 23, 43 prevent one track moving faster than the other trackwhich, in turn, prevents slippage of gripping pads 75. By preventingslippage of gripping pads 75, wear on gripping pads 75 and othercomponents of linear pipe tensioner 10 are reduced. In one suchembodiment, a hydraulic power unit supplies fluid to a set of rotaryflow dividers or gear pumps that are coupled together by a common shaft.One rotary flow divider/gear pump feeds fluid to drive assembly 23, andthe other rotary flow divider/gear pump feeds fluid to drive assembly43. Coupling both rotary flow divider/gear pumps together causesrotation of both flow divider/gear pumps at the same rate. As a result,the same volume of fluid is delivered to drive assemblies 23, 43providing simultaneous action of drive assemblies 23, 43. Thus, frontaxles 21, 41 are rotated at the same. To reduce the likelihood ofcavitation when fluid is pumped in the opposite direction through therotary flow divider/gear pumps, a hot fluid shuttle circuit is disposedbetween the two rotary flow divider/gear pumps.

In another particular embodiment, as illustrated in the schematics ofFIGS. 11-12, the drive motor flow control system includes a transfervalve disposed between the hydraulic power unit which supplies fluid tothe rotary flow divider/gear pumps. The transfer valve permits the flowof fluid to the rotary flow divider/gear pumps to be changed from beingin series (FIG. 11) to being in parallel (FIG. 12), and vice versa. Whenplaced in the “series” mode, the fluid flows from the hydraulic powerunit through the transfer valve, to one of drive assemblies 23, 43, tothe other of drive assemblies 23, 43, back through the transfer valve tothe hydraulic power unit, as illustrated by the clockwise andcounterclockwise arrows between the transfer valve, the upper driveassembly 23, and the lower drive assembly 43 shown in FIG. 11. Forexample, the fluid can flow from the hydraulic power unit through thetransfer valve, to drive assembly 23, to drive assembly 43, back throughthe transfer valve (counterclockwise in FIG. 11), and to the hydraulicpower unit. Alternatively, the fluid can flow from the hydraulic powerunit through the transfer valve, to drive assembly 43, to drive assembly23, back through the transfer valve (clockwise in FIG. 11), and to thehydraulic power unit. Thus, the “series” mode functions as discussedabove to provide synchronization of rotation of front axles 21, 41 suchas during pipe recovery operations.

When placed in the “parallel” mode, as shown in FIG. 12, the fluid flowsfrom the hydraulic power unit through the transfer valve and to driveassemblies 23, 43 simultaneously before being transported back throughthe transfer valve to the hydraulic power unit. Thus, the “parallel”mode allows the two drive assemblies 23, 43 to operate independently ofeach other to provide rapid response and speed from both driveassemblies 23, 43 when demanded such as during pipe lay operations.

To facilitate switching between the “parallel” mode and the “series”mode, the transfer valve is operatively associated with an electronicspackage.

Referring now to FIGS. 3-4, roller assemblies 60 each comprise hydrauliccylinder 61 having hydraulic piston 62 disposed therein. Hydrauliccylinders 61 have hydraulic fluid (not shown) disposed therein. As shownin FIG. 3, hydraulic cylinders 61 comprise upper chamber 70 and lowerchamber 71 divided by divider 72. Divider 72 is in sliding engagementwith the inner wall surfaces of upper and lower chambers 70, 71.Aperture 73 is in fluid communication with lower chamber 71. As shown inFIG. 3, aperture 73 is disposed in the bottom of hydraulic cylinder 61.It is to be understood that aperture 73 is not required to be disposedin the bottom of hydraulic cylinder 61. Connected to aperture 73 is ahose (not shown) that places aperture 73 and, thus, lower chamber 71, influid communication with a reservoir (not shown). Each hose can beconnected to a separate reservoir. Alternatively, the hoses can beconnected to a manifold on the reservoir. Thus, in an embodiment, lowerchambers 71 may function as accumulators to facilitate movement ofhydraulic piston 62 within hydraulic cylinder 61. Alternatively, ifaperture 73 is not disposed in the bottom of hydraulic cylinder 61,hydraulic cylinders 61 may utilize external accumulators (not shown).

Roller assemblies 60 also comprise swivel members 63 to facilitaterotational movement of piston 62, roller carriage 64 pivotally connectedto an upper end of piston 62 for pivotal movement of roller carriages 64and, thus, rollers 66. Roller carriages 64 are pivotally connected toeach other such as by bar 67 having slots 68 for receiving pins 69 thatare secured to roller carriages 64.

In the arrangement shown in FIGS. 3-4, cylinders 61 and pistons 62provide up and down movement of rollers 66, swivel members 63 providerotational movement of rollers 66, and roller carriages 64 and bar 67provide longitudinal pivoting of rollers 66 between adjacent rollercarriages 64. Therefore, this arrangement provides tracks 24, 44 to becompliant or adjustable as the pipe segment linearly moves throughlinear pipe tensioner 10 so as to adjust for any changes in shape orouter diameter size of the pipe segment caused by such items as cement,biological growth, anodes, valves, bent portions of the pipe segment,and the like as those portions of the pipe segment pass through linearpipe tensioner 10.

Referring now to FIGS. 5-10, in one embodiment of gripping pads 75,gripping pad 75 comprises gripping member plate 80, top plate 90, andcompliant member 92. Gripping member plate 80 comprises bottom surface81, top surface 82 (best shown in FIGS. 8-10), two longitudinal sidesurfaces 83, and two lateral side surfaces 84. In the embodiment ofFIGS. 5-10, top plate 90 includes shoulder 91 running the length of oneof the two longitudinal side surfaces of top plate 90 to facilitateplacement of gripping pad 75 on tracks 24, 44 at the desired ornecessary orientation to facilitate gripping pad 75 engaging the pipesection so that the pipe section can be pulled through linear pipetensioner 10. Top plate 90 also includes one or more slots (not shown)for receiving gripping members, such as gripping members 100 discussedin greater detail below.

Disposed on an upper surface of top plate 90 is compliant member 92.Compliant member 92 can be bonded or molded to the upper surface of topplate 90. Compliant member 92 can be formed out of any material that,when placed under load, can compress and, when the load is removed,return toward its original configuration. In one particular embodiment,compliant member 92 is formed out of a resilient, elastomeric orpolymeric material of a commercially available type that will withstandhigh temperatures that occur in some wells. Preferably, the durometerhardness of material forming the compliant member 92 is in the rangefrom about 60 to 100 Shore A and more particularly from 80 to 90 ShoreA. In one embodiment, the durometer hardness is about 85 Shore A.

Compliant member 92 comprises a bottom surface that is engaged with theupper surface of top plate 90, top surface 93, two longitudinal sidesurfaces 94, and two lateral side surfaces 95. Compliant member 92includes one or more slots 96 for receiving gripping members 100(discussed in greater detail below with respect to FIGS. 8A-10C). In theembodiment of FIGS. 5-10C, compliant member 92 also includes grooves 97,98 to permit access to two of the fastener openings 110 disposed throughtop plate 90 and gripping plate member 80 to facilitate securinggripping pads 75 to tracks 24, 44. In the embodiment shown in FIGS.5-10, top surface 93 of compliant member 92 also includes beveledportion 99 to facilitate gripping the pipe (not shown).

Referring now to FIGS. 8A-8C, an embodiment is shown where grippingmember plate 80 comprises three identical gripping members 100. Grippingmembers 100 comprise an upper end 101, a lower end 102, and length 104,width 106, and a height 108. Upper end 101 includes chamfers 103 toprovide a point at upper end 101. As shown in the specific embodimentsof FIGS. 8-10, gripping members 100 are rectangular-shaped and disposedat non-right angles relative to both the longitudinal axis and thelateral axis of gripping member plate 80.

Length 104, width 106, and height 108 may be any measurement desired ornecessary to facilitate gripping the pipe segment when gripping pad 75engages the pipe segment. As shown in FIG. 5, in this particularembodiment height 108 is such that gripping members 100 do not protrudeout of slots 96 of compliant member 92 when gripping pad 75 is notengaged with the pipe segment. In one particular embodiment, grippingmembers 100 are rectangular-shaped having length 104 in the range from1.75 inches to 2.25 inches, width in the range from 0.60 inches to 0.85inches, and height 108 in the range from 2.5 inches to 2.75 inches. Inspecific embodiments, upper ends 101 of gripping members 100 do notprotrude out of slots 96 to facilitate protecting upper ends 101 frombeing damaged, prior to gripping pad 75 engaging a pipe segment andcompliant member 92 being compressed to expose upper ends 101 ofgripping members 100. In certain of these embodiments, the height ofslots 96 can be approximately 10-15% longer in length as compared toheight 108. Thus, in embodiments where height 108 is in the range from2.5 inches to 2.75 inches, slots 96 have a height in the range from 2.75inches to 3.1625 inches.

Referring now to FIGS. 9A-9C, an alternative embodiment to FIGS. 8A-8Cis shown where gripping member plate 80 comprises three identicalgripping members 100. In this embodiment, gripping members comprise alower end 102 and an upper end 105 distinct from upper end 101 depictedin the embodiment of FIG. 8A-8C in that it is radiused rather thanchamfered to a point. As mentioned above, gripping member plate 80 andtop plate 90 include a number of fastener holes 110 for receivingfasteners (not shown) to secure top plate 90 to gripping member plate 80and to secure gripping member plate 80 to tracks 24, 44.

Referring now to FIGS. 10A-10C, yet another alternative embodiment isshown where gripping member plate 80 comprises three identical grippingmembers 100. In this embodiment, gripping members 100 and grippingmember plate 80 are cast as a unitary piece with gripping membersprotruding from gripping member plate with no distinct lower end. Upperends 107 of gripping members 100 are rectangular in shape andadditionally feature a knurled surface for additional gripping strength.Further alternative embodiments may feature roughened surfaces, groovedsurfaces, spiked surfaces, and other surfacing techniques designed toincrease grip.

Although gripping member plate 80 is shown as having three identicalgripping members 100 for simplicity, it is to be understood that thenumber of gripping members 100 and the shapes, and sizes of grippingmember 100 is not required to be identical. To the contrary, eachgripping member 100 can be different in shape and size as compared tothe other gripping members 100. For instance, a single embodiment couldalternate between the chamfered gripping members shown in FIG. 8A-8C andthe rounded gripping members shown in 9A-9C. In addition, the number ofgripping members 100 can be any number desired or necessary to providesufficient gripping engagement with the pipe segment disposed withinarea 30 of linear pipe tensioner 10. For example, one, two, or fourgripping member(s) 100 may be disposed on gripping member plate 80.Alternatively, one or more of the gripping members 100 could becylindrically shaped rather than rectangular shaped. In addition, thetip(s) of each gripping member 100 can comprise a hardened material,such as carbide, to further facilitate gripping the pipe segment.

Broadly, in one specific embodiment of an operation using the linearpipe tensioners disclosed herein, a pipe segment is disposed between theupper and lower tracks by pivoting the upper track from a closedposition to an opened position. Upon being disposed between the upperand lower tracks, the drive assemblies are actuated either in parallelmode or series mode as discussed above. In so doing, the pipe segment,which can be a series of pipe joints forming a pipeline, is movedlinearly through the linear pipe tensioner to either recover pipelinefrom the ocean or to lay pipeline on the ocean floor. During operationof certain of the linear pipe tensioners, one or more roller assembliesoperatively associated within the upper track and/or the lower track,move, pivot, and/or rotate to accommodate fluctuations in the outerdiameter of the pipeline being moved through the linear pipe tensioner.In addition, gripping pads having one or more gripping members disposedthrough a compliant member engage the pipeline, such as due to thecompression of the compliant member, to facilitate linear movement ofthe pipeline through the linear pipe tensioner.

It is to be understood that the invention is not limited to the exactdetails of construction, operation, exact materials, or embodimentsshown and described, as modifications and equivalents will be apparentto one skilled in the art. For example, the gripping members are notrequired to have sharpened upper ends, nor are they required to berectangular-shaped as shown in the Figures. Instead, the grippingmembers can be spikes with or without sharpened upper ends, or any othershape desired or necessary to provide adequate gripping of the pipesegment. In addition, as discussed above, the gripping members 100 arenot required to be identical in shape or size and can be as few as oneor as many as desired or necessary to facilitate gripping of the pipesegment. Further, the pivot assembly is not required to include ahydraulic cylinder, but instead can comprise a swivel member such as aball joint, or other hinge assembly. Moreover, the roller carriages canbe pivotally connected to one another using devices other than the barand pin connection shown in the Figures, such as ball joints and thelike. Additionally, each roller carriage can include as few as oneroller or three or more rollers instead of the two rollers shown in theFigures. Further, the gripping pads are not required to include both atop plate and a gripping member plate. To the contrary, a single platecan provide the gripping members and can receive the compliant member.Accordingly, the invention is therefore to be limited only by the scopeof the appended claims.

What is claimed is:
 1. A linear pipe tensioner comprising: a framehaving an upper frame member and a lower frame member, the upper framemember being pivotally secured to the lower frame member, the upperframe member having a closed position and a plurality of openedpositions; an upper track assembly having an upper track operativelyassociated with two upper axles, the upper track assembly being securedto the upper frame member; a lower track assembly having a lower trackoperatively associated with two lower axles, the lower track assemblybeing secured to the lower frame member below the upper track to definea pathway between the upper track and the lower track; and a pivotassembly, wherein the pivot assembly is operatively associated with theupper frame member and the lower frame member, and wherein the pivotassembly pivots the upper frame member from the closed position towardone of the plurality of opened positions and from the plurality ofopened positions toward the closed position.
 2. The linear pipetensioner of claim 1, wherein the pivot assembly comprises a hydrauliccylinder pivotally connected to the lower frame.
 3. The linear pipetensioner of claim 2, wherein the pivot assembly further comprises twohinge members, each hinge member comprising a bracket and a pin.
 4. Alinear pipe tensioner comprising: a frame; a first track assembly havinga first track operatively associated with two first track axles, thefirst track assembly being secured to the frame; a second track assemblyhaving a second track operatively associated with two second trackaxles, the second track assembly being secured to the frame above thefirst track to define a pathway between the first track and the secondtrack for receiving a pipe; and a first roller assembly operativelyassociated with the first track, the first roller assembly having afirst roller operatively associated with a first roller carriage,wherein the first roller carriage is pivotally connected to a firsthydraulic piston operatively associated with a first hydraulic cylinder.5. The linear pipe tensioner of claim 4, wherein the first hydrauliccylinder is operatively associated with a swivel member for rotationalmovement of the first hydraulic piston.
 6. The linear pipe tensioner ofclaim 4, further comprising a second roller assembly operativelyassociated with the first track, the second roller assembly comprising asecond roller operatively associated a second roller carriage, thesecond roller carriage being pivotally connected to a second hydraulicpiston that is operatively associated with a second hydraulic cylinder,wherein the first roller carriage is pivotally connected to the secondroller carriage.
 7. The linear pipe tensioner of claim 6, wherein thefirst roller carriage is pivotally connected to the second rollercarriage by a bar having a first slot and a second slot, the first slotoperatively associated with a first pin operatively associated with thefirst roller carriage and the second slot operatively associated with asecond pin operatively associated with the second roller carriage. 8.The linear pipe tensioner of claim 4, further comprising a second rollerassembly operatively associated with the second track, the second rollerassembly having a second roller operatively associated a second rollercarriage, the second roller carriage being pivotally connected to asecond hydraulic piston operatively associated with a second hydrauliccylinder.
 9. The linear pipe tensioner of claim 4, wherein the firsttrack comprises a plurality of first track roller assemblies operativelyassociated with the first track, each of the first track rollerassemblies having a roller operatively associated a roller carriage, theroller carriage being pivotally connected to a hydraulic pistonoperatively associated with a hydraulic cylinder, and wherein the secondtrack comprises a plurality of second track roller assembliesoperatively associated with the second track, each of the second trackroller assemblies having a roller operatively associated a rollercarriage, the roller carriage being pivotally connected to a hydraulicpiston operatively associated with a hydraulic cylinder.
 10. The linearpipe tensioner of claim 4, further comprising a first drive assemblyoperatively associated with at least one of the two first track axles, asecond drive assembly operatively associated with at least one of thetwo second track axles, the first and second drive assemblies being influid communication with a hydraulic motor through a transfer valve, andwherein the transfer valve comprises a first setting in which ahydraulic fluid flows simultaneously to the first and second driveassemblies, and a second setting in which the hydraulic fluid flows tothe first or second drive assembly and then to the other of the first orsecond drive assembly, the transfer valve being actuatable between thefirst and second settings.
 11. A linear pipe tensioner comprising: aframe; a first track assembly secured to the frame, the first trackassembly having a first track operatively associated with two firsttrack axles, the first track having a first gripping pad, the firstgripping pad having a first compliant member having a first slot and afirst gripping member disposed within the first slot; and a second trackassembly having a second track operatively associated with two secondtrack axles, the second track assembly being secured to the frame abovethe first track to define a pathway between the first track and thesecond track for receiving a pipe.
 12. The linear pipe tensioner ofclaim 11, wherein the first gripping member protrudes through the firstslot during compression of the first compliant member.
 13. The linearpipe tensioner of claim 12, wherein the first gripping member is fullydisposed within the first slot prior to compression of the firstcompliant member.
 14. The linear pipe tensioner of claim 13, wherein thefirst gripping member is disposed on a first gripping member plate withthe first gripping member being disposed within the first slot of thefirst compliant member.
 15. The linear pipe tensioner of claim 11,wherein the first gripping pad comprises a plurality of grippingmembers, each of the plurality of gripping members being disposed in acorresponding slot within the first compliant member.
 16. The linearpipe tensioner of claim 15, wherein each of the plurality of grippingmembers is disposed at a non-right angle relative to a lateral axis anda longitudinal axis of the first gripping pad.
 17. The linear pipetensioner of claim 11, wherein the second track includes a secondgripping pad, the second gripping pad having a second compliant memberhaving a second slot and a second gripping member disposed within thesecond slot.
 18. The linear pipe tensioner of claim 11, wherein thefirst track includes a plurality of first track gripping padsoperatively associated with the first track, each of the first trackgripping pads having a compliant member having a slot and a grippingmember disposed within the slot, and wherein the second track includes aplurality of second track gripping pads operatively associated with thesecond track, each of the second track gripping pads having a compliantmember having a slot and a gripping member disposed within the slot. 19.A method for linear transport of a pipe segment, the method comprisingthe steps of: (a) placing a pipe segment between a first track and asecond track of a linear pipe tensioner, the first track operativelyassociated with a first drive assembly and the second track operativelyassociated with a second drive assembly, the first and second driveassemblies operatively associated with a hydraulic power unit and avalve disposed between the first and second drive assemblies and thehydraulic power unit, the valve having a first valve position in which ahydraulic fluid flows to the first and second drive assembliessimultaneously, and a second valve position in which the hydraulic fluidflows from either the first drive assembly to the second drive assemblyor the second drive assembly to the first drive assembly; (b) actuatingthe first and second drive assemblies causing the pipe segment to movelinearly through the first and second tracks; and (c) modifying therotation of the first and second tracks by actuating the valve fromeither the first valve position to the second valve position or from thesecond valve position to the first valve position.
 20. The method ofclaim 19, wherein during step (b), a plurality of compliant membersdisposed on corresponding gripping pads are compressed causing aplurality of gripping members to engage the pipe segment.
 21. The methodof claim 19, wherein during step (b), at least one of either the firsttrack or the second track moves vertically in response to a change in anouter diameter of the pipe segment.
 22. The method of claim 19, whereinduring step (b), at least one of either the first track or the secondtrack rotates in response to a change in an outer diameter of the pipesegment.
 23. The method of claim 19, wherein during step (a), the firsttrack is moved pivotally in a first direction from a closed position toan opened position to facilitate placement of the pipe segment betweenthe first and second tracks and then moved pivotally in a seconddirection from the opened position to the closed position to engage thefirst track with the pipe segment.
 24. The method of claim 19, whereinduring step (c), the valve is actuated from the first valve position tothe second valve position.
 25. The method of claim 19, wherein duringstep (c), the valve is actuated from the second valve position to thefirst valve position.